Having people move out of the Amazon appears to boost the risk of fires.

Fire has been used as an agricultural management tool for millennia. It helps to combat pests, weeds and disease, clears debris, and recycles nutrients in the soil. But over the last decade, destructive fires have been taking their toll on the Amazon. These fires lead to forest degradation, release stored carbon into the atmosphere, impair air quality, and damage property.

While previous studies have found that drought and proximity to roads increase the frequency of fires, a team of researchers from Columbia University and the Center for International Forestry Research have found a new cause. Their study, published in the Proceedings of the National Academy of Sciences, found that decreases in rural populations is an additional factor in the increased incidence of fires.

Factors that contribute to fires are poorly understood, and climate variability has only made the picture murkier. Climate is changing patterns of drought and humidity. Severe droughts hit Amazonia in 2005 and 2010, and agriculture-related fires became a major problem in their aftermath. In addition to drought, increased fire risk in the Peruvian Amazon is likely due to a several factors that interact with drought severity, such as increased flammability of forests due to timber extraction, and the repeated burning for extension of roadways.

In addition to physical factors, economic factors also influence increased fire risk. Policies that stimulate agricultural development and road construction provide farmers with economic incentives and access to develop the land, and they have led to increased fire activity elsewhere in the Amazon.

The researchers analyzed climate, remote sensing, province-level census data, and farmer surveys to determine the contributions of climate, land use patterns, and socioeconomic factors (namely rural migration) on fire activity. Farmer surveys were collected in 2010 for 37 communities in a smaller focus area, and looked at things like population density, land use, location of residence of land owners, and degree of implementation of fire control methods. These surveys also provided data on the frequency and extent of burn scars, bare patches of ground where some of the vegetative cover has been burned off by either controlled or uncontrolled fires.

This smaller regional model revealed that the occurrence and location of fires was associated with drought severity, proximity to roads and rivers, and the extent of pastures and agricultural crops. In areas where agricultural crops covered more than 20 percent of the land area, fire risk more than doubled from wet to dry years.

The association of fires with economic activity might lead you to expect that having more people in rural areas would increase fire risk. But, contrary to that, the researchers discovered that declining rural populations at the provincial scale were associated with greater fire frequency and larger burn scars. The decline in rural populations and expansion of road infrastructure, when combined with an increasingly unpredictable climate, signal greater damage from fire in the future.

Although several initiatives have been implemented to avoid or minimize the risks associated with agricultural fires, these policies won’t be effective unless they address the factors that contribute to the fires. The authors note that the implementation of early warning systems could reduce the risk to humans and ecosystems, and policies that promote low-fire land use in areas where land owners are often absent, could also reduce the damage.

14 Reader Comments

This is a curious article: I'm left wondering whether Amazon fires are a significant problem today and whether they are considered generally good or bad. The article indicates that attempts are being made to create early warning systems for the protection of humans and ecosystems - but are some fires still seen as good?

I'm thinking in particular of Yosemite where initially Park Management attempted to reduce forest fires. They found out later that the giant redwoods actually required the fires for propagation.

I wonder if this study accounted for the massive illegal burning, land-grabbing tactics that persist in many Amazonian countries? If the fat cat agricultural mafia can't get access to forested land, the next best thing to do is burn it. Classic land-grab tactic, very common in Africa as well.

"See, this is the kind of carbon emissions that we need to stop; not frickin' 100W lightbulbs!"

And you would be correct if only we were talking about one light bulb. If you, and everyone else, were to stop using light bulbs, and I only used one, there certainly wouldn't be a problem with me choosing an inefficient 100 watt bulb. How many billions of light bulbs burn in the world? Are you willing to give up all of your light bulbs so I can keep the inefficient one?

I really wish schools still taught multiplication so this kind of error wouldn't be so common...

I know that one of the issues with forestland management in the US is that the forests don't get burned back as often as the do when left alone, because we keep putting the fires out. Even outside of forestland, in the central-west Texas area I'm from mesquite trees are taking over. However, one beneficial side effect of the fires the last couple of years is a major reduction in the mesquite population.

So I'm curious if there's been a study that says "Really, given X conditions we should torch the forest every Y years". It seems to be that given that knowledge, it would be a relatively simple thing to do the burns a section at a time with proper firebreaks and the like, and might well reduce the number of incidental fires by turning a lot of the flammables (e.g. leaf mulch on the surface) to nice, nutritious (for plants) ash.

Other sources I've read indicate that land-grabs are the biggest reason for the fires. Agricultural firms and mining companies have been doing the most burning. You burn some farmer's land, what is he going to do? Stay until they kill him? Most of the small farmers are moving to the cities because the big firms are basically shoving the farmers off their land.

It's mostly inferred in the article itself that these aren't wildfires, but are in fact either directly or indirectly manmade. It's the fact that this seems to be correlating with a decrease in rural population that's notable, because it's at odds with what you'd expect the trend to be. As other posters have mentioned this is most likely due to small scale individual farmers being pushed out to make way from corporate firms.

I spoke about this with an aboriginal elder once, when I was a kid (he passed away years ago).

His people used to burn all their land frequently, usually twice a year. That way it's a small fire, grass and weeds only. Trees don't burn unless they have been dead for a few years already and animals simply jump over the line of fire, or run away until they find a boulder or something. The grass grows back within a week, but weeds take several months.

Now he's gone; instead of small knee high fires all the time there are massive infernos that kill all but the biggest trees are too ferocious for animals to avoid without injury or death.

Park rangers are slowly starting to learn, but they still don't burn often enough. Either because they think burning is a bad idea or because someone above them doesn't allow them to do it.

"See, this is the kind of carbon emissions that we need to stop; not frickin' 100W lightbulbs!"

And you would be correct if only we were talking about one light bulb. If you, and everyone else, were to stop using light bulbs, and I only used one, there certainly wouldn't be a problem with me choosing an inefficient 100 watt bulb. How many billions of light bulbs burn in the world? Are you willing to give up all of your light bulbs so I can keep the inefficient one?

I really wish schools still taught multiplication so this kind of error wouldn't be so common...

It's not simple multiplication. Many light fixtures need to be replaced or they will burn out the LED and CFC style bulbs much more rapidly than the "average" life of the newer style bulbs. So you have to factor in either the increased replacement rate or the hidden costs associated with fixture and wiring replacement. Consider the costs of dealing with lead paint and asbestos just as one example. Another example is in various forms of outdoor lighting- I have an exterior lamp which will require installation of some type of heating element if I don't want to replace the CFC or LED bulbs about once a week during the winter when it's -50(F) outside.

I'm all for making things more energy efficient, but frankly speaking the legal mandate was a little bit premature and largely not necessary as people were already starting to shift to more efficient styles on their own.

Being Brazilian and keeping track of stuff that happens at the Amazon Forest, most of the time fires are started either by illegal miners, illegal woodsmen (to divert attention) or by cattle farmers, as a quick way to clear the land for grass.Our nearly inert government tackles the issue by waiting around until there's no more forest to worry about. It IS hard to keep track of what's going on around such a large area, so much that we use our Air Force to patrol and recon the area.

I must also note that, despite firearms being completely outlawed for civilians in our country, most places in the northern regions are filled to the brim with armed militias. It's almost a no man's land.

On the plus side, our government is proud to announce that the percentage of deforesting is the lowest in 10 years. Well, there's not much forest left to deforest, so the percentage is bound to go down.

I must also note that, despite firearms being completely outlawed for civilians in our country

No they aren't. Don't you remember the 2008 referendum on the ban of firearm sales?Guns are strictly controlled, owning a gun requires a permit issued by the Federal Police or the Army, but such permits are usually granted(assuming no criminal precedents).

Perhaps you're thinking of the almost absolute ban on carying weapons. Getting a license to carry a weapon is pretty much impossible unless your job requires it.

Yes there is a lot of armed criminal activity in the the northern states, but saying the place is filled to the brim with armed militias is absurd, the Brazilian amazon is mostly void of people.

While I agree that the government is doing nearly enough to protect the forest, the percentage of deforesting being the lowest is relevant no matter how much the forest has already been burned, it's a percentage, not an abolute number.

Allie Wilkinson / Allie is a freelance contributor to Ars Technica. She received a B.A. in Environmental Studies from Eckerd College and a Certificate in Conservation Biology from Columbia University's Earth Institute Center for Environmental Sustainability.